"Customize" (just one "o") is available in Cydia. Just open up Cydia and search for customize.
Although, it doesn't seem to work on the 2nd generation iPod touch. For adding themes (off of DeviantART.com or Macthemes) and modifying icons and whatnot, download OpenSSH from Cydia, and find a tutorial on the internet to connect to your iPod touch from your computer. (I made a tutorial on this, search fswmacguy on YouTube.)